Showing papers by "Xinhua Wu published in 2005"
TL;DR: In this article, a finite element model has been established and used to predict the temperature history of direct laser fabricated (DLFed) Ti-6Al-4V thin wall samples, and the effects of laser power and the effect of location within a sample on its temperature history have been modeled and compared with temperatures measured during DLF using thermocouples.
Abstract: A finite element model has been established and used to predict the temperature history of direct laser fabricated (DLFed) Ti–6Al–4V thin wall samples. The effects of laser power and the effect of location within a sample on its temperature history have been modelled and compared with temperatures measured during DLF using thermocouples. The thermal history of the material has been correlated with the observed differences in the microstructures obtained at different locations in a given sample or for a given location in samples obtained at different laser powers.
132 citations
TL;DR: In this paper, the room temperature tensile properties of a number of cast TiAl-based alloys, which have been grain-refined either by additions of boron or by a new quenching and ageing treatment, have been assessed.
84 citations
TL;DR: In this article, the effects of complex loading on fatigue strength have also been investigated with pre-creep deformations of 0.5, 3 and 5%, pre-exposure to 700 Â c for 24 and 150 Â h or pre-low cycle fatigue testing at 700 Ã c.
84 citations
TL;DR: In this article, a new fine microstructure with significantly improved tensile properties can be generated in massively transformed, quenched and tempered samples of TiAl-based alloys.
73 citations
TL;DR: In this paper, the effects of the casting conditions, including superheat, rotation speed at one mould temperature have been investigated in terms of the product integrity and porosity and the microstructure of the valves.
69 citations
TL;DR: In this paper, the influence of carbon addition on the aging response of quenched Ti-13wt. % Cr has been investigated using hardness tests, tensile tests, optical microscopy, scanning electron microscopy and transmission electron microscope.
Abstract: The influence of carbon addition on the aging response of quenched Ti-13wt. % Cr has been investigated using hardness tests, tensile tests, optical microscopy, scanning electron microscopy, and transmission electron microscopy. The addition of carbon improves the homogeneity of α precipitation, reduces the growth rate of α, and greatly reduces grain boundary α precipitation. The carbon addition accelerates the rate at which hardening occurs during aging, increases the peak hardness of aged samples, and also increases the room temperature tensile strength and ductility of aged samples. The factors giving rise to the improvements in properties will be discussed in terms of the microstructural observations.
25 citations
TL;DR: In this paper, Widmanstatten microstructures with angles of about 30, 64 and about 90° with respect to the matrix lamellar colonies were observed with the majority of them making an angle of about 64°.
15 citations
TL;DR: In this article, the role of oxygen and carbon additions and deformation on aging kinetics are discussed in terms of the factors, such as ω, dislocations, and grain boundary oxygen content that influence α precipitation.
Abstract: Optical microscopy, analytical transmission microscopy and scanning electron microscopy, and hardness tests have been carried out on quenched samples of Ti-15wt.%V-3wt.%Cr-3wt.%Al-3wt.%Sn containing different levels of oxygen and carbon that were aged at temperatures between 400 and 600 °C. The increase of oxygen content and the addition of carbon (C) increase the kinetics and the magnitude of age hardening. The addition of C greatly reduces the coarse grain boundary precipitation of α. Room temperature deformation has been shown to override compositional differences, and all deformed alloys age harden similarly. The role of oxygen and carbon additions and deformation on aging kinetics are discussed in terms of the factors, such as ω, dislocations, and grain boundary oxygen content that influence α precipitation.
9 citations
TL;DR: In this article, the influence of the imposed strain rate on the stress-strain response of Ti64 and Ti550 alloys is found to be very similar, the yield stress increases with increase of strain rate and the energy absorbed to fracture increases.
Abstract: The stress-strain response of samples of Ti64 and Ti550 at strain rates from 10−1 s−1 to 103 s−1 and samples of Ti811 and Ti153 at a strain rate of 103 s−1 have been assessed. It has been found that the influence of the imposed strain rate on the stress-strain response of Ti64 and Ti550 alloys is very similar – in both alloys the yield stress increases with increase of strain rate and the energy absorbed to fracture increases. At high strain rates localised deformation occurs in the form of shear bands in Ti64 and Ti550 but no shear banding was seen in Ti811 and Ti153. The fracture surfaces of Ti64 and of Ti550 show an increased tendency to brittle failure and an increase in necking with increase of strain rate. The influence of alloy microstructure and composition on the response to changes in imposed strain rate are discussed in terms of adiabatic heating and the factors controlling the flow stress in these alloys.
8 citations
01 Dec 2005
TL;DR: In this article, two types of feedstock were fed simultaneously into the laser focal point, a burn resistant (BurTi) alloy Ti-25V-15Cr-2Al-0.2C powder and a Ti-6Al-4V wire.
Abstract: A compositionally graded material has been fabricated using Direct Laser Fabrication. Two types of feedstock were fed simultaneously into the laser focal point, a burn resistant (BurTi) alloy Ti-25V-15Cr-2Al-0.2C powder and a Ti-6Al-4V wire. The local composition of the alloy was changed by altering the ratio of powder to wire by varying the feed rate of the powder whilst maintaining a fixed feed rate of wire-feed. For the range of compositions between about 20% and 100% BurTi only beta was observed and the composition and lattice parameter varied monotonically. The grain size was found to be much finer in these functionally graded samples than in laser fabricated Ti64. Some samples were made using the wire-feed alone, where it was found that the microstructure is different from that found when using powder feed alone. The results are discussed in terms of the power requirements for laser fabrication of powder and wire samples.A compositionally graded material has been fabricated using Direct Laser Fabrication. Two types of feedstock were fed simultaneously into the laser focal point, a burn resistant (BurTi) alloy Ti-25V-15Cr-2Al-0.2C powder and a Ti-6Al-4V wire. The local composition of the alloy was changed by altering the ratio of powder to wire by varying the feed rate of the powder whilst maintaining a fixed feed rate of wire-feed. For the range of compositions between about 20% and 100% BurTi only beta was observed and the composition and lattice parameter varied monotonically. The grain size was found to be much finer in these functionally graded samples than in laser fabricated Ti64. Some samples were made using the wire-feed alone, where it was found that the microstructure is different from that found when using powder feed alone. The results are discussed in terms of the power requirements for laser fabrication of powder and wire samples.
3 citations
01 Jan 2005
01 Dec 2005
TL;DR: A 2D axis-symmetric-transient finite element model for direct laser fabrication has been developed for predicting the temperature history of Direct Laser Fabricated (DLFed) Ti-6Al-4V thin wall samples.
Abstract: A 2D axis-symmetric-transient finite element model for direct laser fabrication has been developed for predicting the temperature history of Direct Laser Fabricated (DLFed) Ti-6Al-4V thin wall samples. The effect of location, laser scanning speed and laser power on the variation of temperature with time have been modelled and compared with temperatures measured using thermocouples during laser fabrication. The microstructures of the laser fabricated Ti-6Al-4V have also been assessed systematically under a range of process conditions. The thermal history of the material has been correlated with the observed differences in the microstructures obtained at different positions within the samples under those processing conditions. It has been found that the predicted thermal histories are in good agreement with those obtained from measurement and the differences observed in microstructures are also consistent with those expected on the basis of the predicted thermal histories of the samples at given locations.A 2D axis-symmetric-transient finite element model for direct laser fabrication has been developed for predicting the temperature history of Direct Laser Fabricated (DLFed) Ti-6Al-4V thin wall samples. The effect of location, laser scanning speed and laser power on the variation of temperature with time have been modelled and compared with temperatures measured using thermocouples during laser fabrication. The microstructures of the laser fabricated Ti-6Al-4V have also been assessed systematically under a range of process conditions. The thermal history of the material has been correlated with the observed differences in the microstructures obtained at different positions within the samples under those processing conditions. It has been found that the predicted thermal histories are in good agreement with those obtained from measurement and the differences observed in microstructures are also consistent with those expected on the basis of the predicted thermal histories of the samples at given locations.
Patent•
17 Mar 2005
TL;DR: In this paper, a hot isostatic pressure bonding/forming process suitable for an integrally bladed disc assembly was proposed, in which pre-formed blades 6 were joined to the circumference of a disc 4, and a cavity was defined at the joint location, filled with alloy powder and hot isstatic pressure was applied to consolidate the powder into a union piece 10 to form the joint 11 in which the consolidated powder is joined to both the disc 4 and the blade 6.
Abstract: In a hot isostatic pressure bonding/forming process suitable for an integrally bladed disc assembly 2 in which pre-formed blades 6 are joined to the circumference of a disc 4, a cavity is defined at the joint location, filled with alloy powder and hot isostatic pressure is applied to consolidate the powder into a union piece 10 to form the joint 11 in which the consolidated powder is joined to both the disc 4 and the blade 6. A number of blades 6 may be joined simultaneously at locations spaced apart around the disc circumference.
Patent•
04 Oct 2005TL;DR: In this article, an aerofoil blade is formed from a first component comprising a void region filled with a salt by joining the first component to a second component using pressure and then removing the salt by melting.
Abstract: A method of forming a product from a first component comprising a void region filled with a salt by joining the first component to a second component using pressure and then removing the salt by melting. Figure 1 shows an aerofoil blade 1 with a plurality of passages 3. The passages 3 are filled with a powdered salt 4 and then welded closed. An end of the blade 1 is located in an end of a mould 2 which is filled with a powdered alloy 6. The blade 1 and mould 2 are hot isostatically pressed, thereby sintering the powder 6 and joining it to the blade 1. The welds 5 are then opened and the salt 4 removed. Figure 2 shows powder preform 26 which comprises a cavity 23. A reinforcing box, web, rib or mesh 20 lies within the cavity 23, along with a salt 24. The perform 26 is hipped and then the salt 24 removed through a drain hole 28 drilled into the body. An alloy may be used instead of a salt.